Magnetic storage disk drive devices are commonly used in computers and data processing systems for storing information in digital form. Digital information is magnetically stored on a recording surface of the magnetic storage disk by selective magnetic polarization of regions of the surface of the disk. The surface of the magnetic storage disks is typically divided into a plurality of concentric storage tracks, where the tracks are numbered to provide addresses for accessing data on the recording surface. Data is accessed as the storage disk rotates by positioning a transducer or read/write head over the surface of the magnetic storage disk with an actuator assembly or apparatus.
Two conventional types of actuator assemblies are linear actuators and rotary actuators. A linear actuator is moved radially with respect to the surface of the magnetic storage disk by means of an actuator pulse system during track selection. A rotary actuator is rotatably mounted adjacent to the magnetic storage disk, and is moved along an arcuate path by energization of a coil placed in a magnetic field. A rotary actuator apparatus typically includes a carriage or support arm structure rotatably mounted on a hub or shaft. At one end of the support arm, a flat coil is attached and disposed relative to the magnetic field. At a distal end, the support arm includes a mounting surface, typically having an aperture, in which a suspension for a read/write head is mounted.
There are a number of known methods for mounting the read/write head to the support arm. One such commonly used method is staking, in which a staking member, typically a short tubular stem, is aligned through the mounting surface aperture and through a hole in a head suspension member. The stem of the staking member is then forcibly expanded within the mounting surface aperture of the actuator support arm by driving a ball bearing through the staking member stem. A disadvantage of the staking procedure is that it imposes limitations on the material used for the actuator support arm because the force applied during the staking procedure can cause cracking of the support arm.
Examples of other mounting methods include use of adhesives, screws and clamps. Of the known methods, staking is often used because this mounting method is purely mechanical, and easily implemented. It is only the interference between the staking member and the actuator support arm which holds them together. A disadvantage of using adhesives is that they tend to outgas over long periods of time, which can be detrimental within the interior of the disk drive device, and which can lead to reliability problems. Further, a disadvantage of using screws or clamps is that the additional hardware requires increased spacing, which can lead to additional materials and increased costs. Additionally, the screws or clamps increase the overall weight of the actuator apparatus. The increased weight of the actuator apparatus causes slower access times which are detrimental to operating performance.
As advances in technology continually increase processing speeds of the computers and data processing systems, and increase capacities of the disk drive devices while reducing costs, the actuators must likewise be improved. Fast access to the information stored on the magnetic disk requires an actuator apparatus having a low weight and low inertia with good damping characteristics and increased resonant frequencies.
Conventional actuator assemblies have a support arm or plural support arms typically formed of aluminum, magnesium, or other like metal alloys. Such metals are chosen for their properties of strength and stiffness. However, as access time has become increasingly important, some manufacturers have made the support arms out of ceramic materials, which are lighter in weight yet stiff. A problem with ceramic support arms though, is that while the ceramic materials have the property of high stiffness, they have a low tensile strength which tends to lead to cracking of the arms during the head mounting procedure. A further development has been to form the actuator arms out of a combination of metal and plastic materials, or of a plastic material. Examples of such combination actuator support arms include U.S. Pat. Nos. 5,305,169 and 5,382,851. An example of an all plastic actuator support arm is found in U.S. Pat. No. 5,165,090.
While the use of plastic materials for the actuator support arms has provided improved performance from the actuator assemblies, the existing plastic actuators have certain limitations and lack desirable properties of the metal support arms. Thus, there is restricted use of actuator assemblies with plastic support arms. A problem with the use of plastic for constructing the actuator support arm is that plastic materials typically are not stiff and strong enough to produce accurate and reliable positioning devices. Conventional actuator support arm structures are typically flat elongated components which are individually manufactured then attached to a holding member which attaches to the actuator coil, or attached directly to the actuator coil. When such actuator support arms are constructed out of a plastic material, there is a tendency for deformation of the support arm if the plastic material selected does not have a modulus of elasticity greater than a certain value. If deformation occurs, accurate positioning of the read/write head affixed to the support arm cannot be achieved.
Another problem related to the use of plastic for construction of the actuator support arm is that plastics are generally not strong enough to withstand the process of staking the read/write head to the support arm. As described above, staking is a desirable method of attaching read/write heads to an actuator support arm. However, the process of staking the read/write head to the support arm tends to exert forces resulting in tangential stresses at the mounting surface aperture. In plastic support arms, the tangential stresses are particularly problematic around a weld or knit area occurring at the distal end of the support arm. The knit area is typically a structurally weak area of the plastic support arm. Therefore, when the read/write head is ball staked in the mounting surface aperture, the tangential stresses at the knit area tend to cause the plastic support arm to crack.
An additional problem related to the desire to stake read/write heads to the actuator support arm is that existing plastic support arms do not permit a certain amount of swaging in the head mounting aperture without breakage at the tip of the support arm. When a read/write head is staked in the aperture, it is necessary that the support arm permits some swaging or deformation proximate to the aperture. The ability to permit a required amount of swaging is necessary because the staking process involves forcibly expanding a staking member within the aperture. Consequently, there must be some swaging or deformation of the aperture as the staking member is expanded therein. However, the present actuator support arms constructed out of plastic do not permit the required amount of swaging, and thus, the support arms tend to crack when the read/write heads are staked in the head mounting aperture. Since the staking process is typically performed at the end of the manufacturing process, the cracking of the support arm results in an actuator assembly which cannot be used, and results in increased manufacturing costs.
The performance of the existing actuators is thus limited by inherent properties of the above materials. Thus, there exists a hitherto unsolved need for a reliable, cost effective actuator apparatus which overcomes the problems of the prior art and which has enhanced dynamic performance.